libcamera: pipeline_handler: Return unique_ptr from createInstance

Avoid naked pointer with memory allocation by returning a unique_ptr
from PipelineHandlerFactory::createInstance(), in order to increase
memory allocation safety.

This allows iterating over factories in the CameraManager and unit tests
using const pointers.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

test/ipa/ipa_interface_test.cpp

@@ -52,9 +52,9 @@ protected:
 		ipaManager_ = make_unique<IPAManager>();
 
 		/* Create a pipeline handler for vimc. */
-		std::vector<PipelineHandlerFactory *> &factories =
+		const std::vector<PipelineHandlerFactory *> &factories =
 			PipelineHandlerFactory::factories();
-		for (PipelineHandlerFactory *factory : factories) {
+		for (const PipelineHandlerFactory *factory : factories) {
 			if (factory->name() == "PipelineHandlerVimc") {
 				pipe_ = factory->create(nullptr);
 				break;